The present disclosure relates to fixing devices, image forming apparatuses and belt driving unit, which are used for copiers, printers, facsimile machines, multifunctional peripherals thereof, etc., and particularly relates to a fixing device, an image forming apparatus, and a belt driving unit, which restrict belt meandering.
Image forming apparatuses transfer a toner image formed on an image carrier, such as a photosensitive drum, or the like to a recording medium, convey the recording medium that carries the toner image to a fixing device, and apply heat and pressure to the recording medium in the fixing device, thereby fixing the toner image on the recording medium to the recording medium.
The fixing device may be of belt fixing type in which the toner image on the recording medium is fused using a fixing belt. The fixing device of the belt fixing type includes a fixing belt rotatably wound between a fixing roller and a heating roller and a pressure roller in press contact with the fixing belt so that the toner image is fused to the recording medium during the time when the recording medium passes through a nip part between the fixing belt and the pressure roller.
In the fixing device of the belt fixing type, the fixing belt may move to meander on the rollers in the axial directions of the rollers when the wound fixing belt rotates between the rollers. Such meandering of the fixing belt may accompany fixing failure, such as displacement of the toner image on the recording medium and the like. Further, incessant meandering of the fixing belt may break the edges of the belt.
Under the circumstances, techniques for suppressing meandering of the fixing belt are examined. For example, some fixing device includes a fixing belt wound between a drive roller and a meandering correction roller and a heating roller so that the recording medium is pressed and heated between the fixing belt and the heating roller to fuse the toner image. This fixing device includes a meandering detection sensor in contact with an edge of the fixing belt to detect belt meandering, the meandering correction roller, a meandering correction cam rotated by driving a motor to sway the meandering correction roller, and a clutch that rotates the motor according to a detection result by the meandering detection sensor. When the meandering detection sensor detects meandering of the fixing belt, the clutch is turned on to transmit the rotational force of the motor to the meandering correction cam. This allows the meandering correction cam to start rotating to sway the meandering correction roller in a direction in which meandering of the fixing belt is corrected.
Referring to another fixing device, a fixing belt is rotatably wound between two rollers and a C-shaped meandering preventing member having springiness is fitted in the opposite edges of one of the rollers by utilizing its spring force. The meandering preventing member has a predetermined thickness and is arranged at the opposite sides of one of the rollers with a distance spaced which is slightly larger than the width of the fixing belt. This may retain the edges of the fixing belt to prevent the fixing belt from meandering in the axial direction of the roller.